The present invention pertains to the field satellite antennas, including receiving systems for satellite antennas.
Geosynchronous communications satellites transmit radio signals from a synchronous earth orbit, approximately 22,000 miles above the equator, to an antenna that receives signals on earth. Such antennas may include direct to the home (xe2x80x9cDTHxe2x80x9d) antennas or Very Small Aperture Terminals (xe2x80x9cVSATxe2x80x9d). A DTH antenna is installed at a home and is used to receive analog and digital television signals from a geosynchronous communications satellite. A VSAT is installed at a business or a home and is used to transmit and receive data and voice signals to and from a geosynchronous satellite.
Many receiving antennas are configured to receive two differently polarized signals (e.g., horizontal/vertical linear polarization or left-hand/right-hand circular polarization) transmitted over the same frequency band, thereby effectively doubling the capacity of the available radio spectrum. For example, referring to FIG. 1, a prior art antenna system 10 includes a parabolic reflector 12 and a Neutonian feed horn 14 located at the focus of the reflector 12. The feed horn 14 is configured to receive first and second polarized signals 13 and 15 transmitted by a communications satellite (not shown).
The feed horn 14 includes an orthomode transducer (not shown) configured to isolate the respective polarized signals 13 and 15. The antenna system 10 further includes a switch 16 for selecting one of the respective polarized signals 13 and 15. In particular, the switch 16 has first and second inputs 18 and 20 coupled to the feed horn orthomode transducer via respective transmission lines 22 and 24, with the first polarized signal 13 being conveyed to the switch input 18 and the second polarized signal 15 conveyed to the switch input 20. A switch control 26 is activated to convey one of the respective polarized signals 13 and 15 to a switch output 28, as a selected polarized signal 17. A low noise block down converter (xe2x80x9cLNBxe2x80x9d) 30 having an input 32 coupled to the switch output 28 via a coaxial cable 32 receives the selected polarized signal 17. The LNB 30 amplifies and down converts the selected polarized signal 17 to an intermediate signal 19 that can be demodulated at an output 34 of the LNB 30 by a device, such as, e.g., a modem or digital television.
In order for the antenna system 10 to operate, the signal-to-noise ratio of the intermediate signal 19 appearing at the LNB output 34 must be high enough to allow the intermediate signal 19 to be used. The use of transmission lines between the feed horn 14 and the switch 16, however, introduce significant losses into the selected polarized signal 17, thereby decreasing the signal-to-noise ratio of the resulting intermediate signal 19. This problem is compounded in noise cancellation antenna systems that employ duplicative components to receive parallel signals, such as those described in Lusignan, U.S. Pat. No. 5,745,084 and copending application Ser. No. 08/259,980 filed Jun. 17, 1994, both of which are fully incorporated herein by reference.
The present invention is directed to a receiver unit for use in an antenna system that receives and amplifies respective first and second polarized RF signals to produce respective first and second amplified RF signals, one of which is then selected as a selected amplified RF signal in response to a control signal. In accordance with a further aspect of the invention, a single transmission line is used to convey both the selected amplified RF signal and the control signal to the receiver unit.
In a preferred embodiment, an antenna system includes an antenna unit, a receiver unit, a down converter and a supply. The antenna unit includes a parabolic reflector, a feed horn and an orthomode transducer, which are configured to capture, isolate and transmit respective first and second polarized RF signals to the receiver unit. The receiver unit is coupled to the antenna unit to receive the first and second polarized RF signals. In particular, the receiver unit includes first and second low-noise amplifiers, which amplify the respective first and second polarized RF signals. The receiver unit further comprises a signal selector, which selects one of the respective amplified RF signals in response to a control signal.
The receiver unit is powered by a DC power signal, which is preferably the same as the control signal provided in the form of a DC power/control signal from the supply. The down converter and supply are coupled to the receiver unit via a single transmission line. The selected amplified RF signal is transmitted to the down converter via the transmission line. The down converter down converts the selected amplified RF signal to an intermediate signal. The supply produces the power/control signal, which is transmitted to the receiver unit via the transmission line to provide power and control thereto.
In another preferred embodiment, an antenna system includes a plurality of antenna units and corresponding receiver units, a combiner, a down converter and a supply. Each of the respective antenna units includes a parabolic reflector, a feed horn, a subreflector and an orthomode transducer, which are configured to capture, isolate and transmit respective first and second polarized RF signals to the corresponding receiver unit. Each receiver unit includes first and second low noise amplifiers, which amplify the respective first and second RF signals, and a signal selector, which selects one of the respective amplified RF signals in response to a respective control signal. The receiver units are powered by a DC power signal, which is preferably the same as the control signal provided in the form of a DC power/control signal from the supply.
The combiner is coupled to the receiver units via respective transmission lines, whereby the selected amplified RF signals are transmitted to the combiner. In particular, the combiner combines the selected amplified RF signals and outputs combined amplified RF signal. The down converter and supply are coupled to the combiner via a single transmission line, whereby the combined amplified RF signal is transmitted to the down converter. The down converter down converts the combined amplified RF signal to an intermediate signal. The supply produces the power/control signal, which is transmitted to the respective receiver units via the transmission line and the respective transmission lines to provide power and control thereto.
Other and further objects, features, aspects, and advantages of the present invention will become better understood with the following detailed description of the accompanying drawings.